1. Field of the Invention
The present invention relates to a magneto-resistance effect element which is configured such that a current is flowed in the direction perpendicular to the film surface thereof, a magnetic head, a magnetic recording/reproducing device and a magnetic memory which include the magneto-resistance effect element, respectively.
2. Description of the Related Art
The performance of a magnetic device is extremely developed which is originated from the discovery of a Giant Magnetoresitive Effect (GMR) in a laminated magnetic body. Particularly, since a spin valve film (SV film) is suitable for a magnetic device in structure, and can exhibit the GMR effect effectively and efficiently, the use of the SV film has developed the magnetic device such as a magnetic head and MRAM (Magnetic Random Access Memory).
The “spin valve” film has such a structure as sandwiching a non-magnetic metal spacer layer between two ferromagnetic layers and is configured such that the magnetization of one ferromagnetic layer (often called as a “pinning layer” or “fixed magnetization layer) is fixed by the magnetization of an anti-ferromagnetic layer and the magnetization of the other ferromagnetic layer (often called as a “free layer” or “free magnetization layer”) is rotated in accordance with an external magnetic field (e.g., an medium magnetic field). With the spin valve film, the intended large magneto-resistance effect can be obtained when the relative angle between the pinning layer and the free layer is changed.
A conventional spin valve film is formed as a CIP (Current In Plane)-GMR element where a sense current is flowed parallel to the film surface of the spin valve film. Recently, a TMR (Tunneling MagnetoResistance) element or a CPP (Current Perpendicular to the Plane)-GMR element gathers attention because the TMR element or the CPP-GMR element can exhibit a larger MR effect than the CIP-GMR element. With the TMR element or the CPP-GMR element, a sense current is flowed perpendicular to the film surface of the TMR element or the CPP-GMR element.
With the TMR element, both of the MR effect and the resistance are large so that the S/N ratio may be deteriorated and the transfer rate of HDD may be lowered due to the large resistance. In this point of view, in order to apply the TMR element for an HDD with a surface recording density of 500 Gbpsi or over, it is required that the resistance of the TMR element is lowered under the condition that the MR effect of the TMR element is maintained large. With the CPP-GMR element, in contrast, both of the resistance and the resistance variation degree (MR effect) are extremely small so that the reproducing signal may be lowered due to the small MR effect which is in reverse to the case of the TMR element. Moreover, such a CPP-GMR element as having a spacer layer is proposed. The spacer layer is configured such that minute current paths (Current-confined Paths: CCPs) made of non magnetic metal are formed through an insulating layer. Since the CPP element can exhibit the CCP (Current-confined path) effect, the CPP can reproduce a larger output signal than the normal CPP-GMR element with the non-magnetic spacer layer. In view of the application for a magnetic head requiring high recording density, however, the CPP element can not exhibit a sufficient MR variation degree (MR effect).
In order to realize a larger MR variation degree (MR effect) applicable for high recording density, such a BMR (Ballistic MagnetoResistance) element as utilizing a BMR effect is proposed (refer to Reference No. 1).    [Reference No. 1] JP-A 2003-204095 (KOKAI)
The BMR effect can be recognized when the spacer connecting a pinning layer and a free layer in a conventional spin valve film is made of minute ferromagnetic metallic particles with their respective sizes in several atomic order. It is considered that the origin of the large MR effect relates to (1) the quantization of conductance at minute junctions or (2) the confinement of magnetic wall (magnetization rotating portion) at minute junctions, but can not be clarified at present. Also, various experiments are conducted, but such a formation technique as forming junctions minute enough to exhibit the BMR effect under good repeatability is not proposed so that the intended BMR element can not be formed sufficiently.